The present invention pertains to coated abrasive articles, and particularly to coated abrasive belts with endless, seamless backings containing an organic polymeric binder and a fibrous reinforcing material. Additionally, this invention pertains to methods of making endless, seamless backings for use in coated abrasive belts.
Coated abrasive articles generally contain an abrasive material, typically in the form of abrasive grains, bonded to a backing by means of one or more adhesive layers. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on pulleys, wheels, or drums. Abrasive articles can be used for sanding, grinding, or polishing various surfaces of, for example, steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather, or ceramics.
The backings used in coated abrasive articles are typically made of paper, polymeric materials, cloth, nonwoven materials, vulcanized fiber, or combinations of these materials. Many of these materials provide unacceptable backings for certain applications because they are not of sufficient strength, flexibility, or impact resistance. Some of these materials age unacceptably rapidly. Also, some are sensitive to liquids that are used as coolants and cutting fluids. As a result, early failure and poor functioning can occur in certain applications.
In a typical manufacturing process, a coated abrasive article is made in a continuous web form and then converted into a desired construction, such as a sheet, disc, belt, or the like. One of the most useful constructions of a coated abrasive article is an endless coated abrasive belt, i.e., a continuous loop of coated abrasive material. In order to form such an endless belt, the web form is typically cut into an elongate strip of a desired width and length. The ends of the elongate strip are then joined together to create a xe2x80x9cjointxe2x80x9d or a xe2x80x9csplice.xe2x80x9d
Two types of splices are common in endless abrasive belts. These are the xe2x80x9clapxe2x80x9d splice and the xe2x80x9cbuttxe2x80x9d splice. For the lap splice, the ends of the elongate strip are bevelled such that the top surface with the abrasive coating and the bottom surface of the backing fit together without a significant change in the overall thickness of the belt. This is typically done by removing abrasive grains from the abrasive surface of the strip at one of the ends, and by removing part of the material from the backing of the elongate strip at the other end. The bevelled ends are then overlapped and joined adhesively.
For the butt splice, the bottom surface of the backing at each end of the elongate strip is coated with an adhesive and overlaid with a strong, thin, tear-resistant, splicing media. Although endless coated abrasive belts containing a splice in the backing are widely used in industry today, these products suffer from some disadvantages which can be attributed to the splice.
For example, the splice is generally thicker than the rest of the coated abrasive belt, even though the methods of splicing generally used involve attempts to minimize this variation in the thickness along the length of the belt. This can lead to a region(s) on the workpiece with a xe2x80x9ccoarserxe2x80x9d surface finish than the remainder of the workpiece, which is highly undesirable especially in high precision grinding applications. For example, wood with areas having a coarser surface finish will stain darker than the remainder of the wood.
Also, the splice can be the weakest area or link in the coated abrasive belt. In some instances, the splice will break prematurely before full utilization of the coated abrasive belt. Belts have therefore often been made with laminated liners or backings to give added strength and support. Such belts can be relatively expensive and under certain conditions can be subject to separation of the laminated layers.
In addition, abrading machines that utilize a coated abrasive belt can have difficulty properly tracking and aligning the belt because of the splice. Further, the splice creates a discontinuity in the coated abrasive belt. Also, the splice area can be undesirably more stiff than the remainder of the belt. Finally, the splice in the belt backing adds considerable expense in the manufacturing process of coated abrasive belts.
The present invention is directed to coated abrasive articles, particularly to coated abrasive belts made from endless, seamless backing loops. By the phrase xe2x80x9cendless, seamlessxe2x80x9d it is meant that the backings, i.e., backing loops, used in the belts are continuous in structure throughout their length. That is, they are free from any distinct splices or joints. This does not mean, however, that there are no internal splices in, for example, a fibrous reinforcing layer, or that there are no splices in an abrasive layer. Rather, it means that there are no splices or joints in the backing that result from joining the ends of an elongate strip of backing material.
Thus, the coated, abrasive articles of the invention do not exhibit many of the disadvantages associated with coated abrasive belts made from backing loops containing a splice. The coated abrasive belts of the invention can readily be prepared with substantially the same thickness or caliper along the entire length, i.e., circumference, of the belt. Typically, the thickness of the endless, seamless backing loops of the present invention does not vary by more than about 15% along the entire length of the loop and preferably varies less than 10%, more preferably less than 5% and most preferably less than 2%.
A coated abrasive belt of the present invention includes a backing in the form of an endless, seamless loop, which contains an organic polymeric binder material and a fibrous reinforcing material. Typically, the binder weight in the backing is within a range of about 40-99 wt-%, preferably within a range of about 50-95 wt-%, more preferably within a range of about 65-92 wt-%, and most preferably within a range of about 70-85 wt-%, based on the total weight of the backing. The polymeric binder material can be a thermosetting, thermoplastic, or elastomeric material or a combination thereof. Preferably it is a thermosetting or thermoplastic material. More preferably it is a thermosetting material. In some instances, the use of a combination of a thermosetting material and an elastomeric material is preferable.
The remainder of a typical, preferred, backing is primarily fibrous reinforcing material. Although there may be additional components added to the binder composition, a coated abrasive backing of the present invention primarily contains an organic polymeric binder and an effective amount of a fibrous reinforcing material. The phrase xe2x80x9ceffective amountxe2x80x9d of fibrous reinforcing material refers to an amount sufficient to give the desired physical characteristics of the backing such as reduction in stretching or splitting during use.
The organic polymeric binder material and fibrous reinforcing material together comprise a flexible composition, i.e., flexible backing, in the form of an endless, seamless loop with generally parallel side edges.
The flexible, endless, seamless backing loop includes at least one layer of fibrous reinforcing material along the entire length of the belt. This layer of fibrous reinforcing material is preferably substantially completely surrounded by (i.e., engulfed within) the organic polymeric binder material. That is, the layer of fibrous reinforcing material is embedded or engulfed within the internal structure of the loop, i.e., within the body of the loop, such that there are regions of organic binder material free of fibrous reinforcing material on opposite surfaces of the layer of fibrous reinforcing material. In this way, the surfaces, e.g., the outer and inner surfaces, of the loop have a generally smooth, uniform surface topology.
The fibrous reinforcing material can be in the form of individual fibrous strands or a fibrous mat structure. The endless, seamless loops, i.e., backing loops, of the present invention preferably consist of various layers of individual fibrous reinforcing strands and/or fibrous mat structures incorporated within, i.e., engulfed within, an internal structure or body of the backing. Preferred belts contain, for example, a thermosetting binder, a layer of noninterlacing parallel and coplanar individual fibrous reinforcing strands, and a layer of a fibrous mat structure wherein the fibrous material within one layer does not interlock with the fibrous material within the other layer.
Certain preferred belts of the present invention also contain a preformed abrasive coated laminate. This preformed laminate typically comprise a sheet material, i.e., material in the form of a sheet, coated with abrasive grains. The preformed abrasive coated laminate can be laminated, i.e., attached, to the outer surface of the backing of the present invention using a variety of means, such as an adhesive or mechanical fastening means. This embodiment of the coated abrasive article of the present invention is advantageous at least because of the potential for removing the laminate once the abrasive material is exhausted and replacing it with another such laminate. In this way the backing of the present invention can be reused. The term xe2x80x9cpreformedxe2x80x9d in this context is meant to indicate that the abrasive coated laminate is prepared as a self-supporting sheet coated with abrasive material and subsequently applied to the endless, seamless backing loops of the present invention. Such embodiments typically have a seam in this preformed coated abrasive laminate layer. The backing loop, however, does not contain a seam or joint. Furthermore, the backing loop is not made of preformed and precured layers adhesively laminated together.
The coated abrasive backings of the present invention are prepared by: preparing a loop of liquid organic binder material having fibrous reinforcing material therein, in extension around a periphery of a support structure, such as a drum; and solidifying the liquid organic binder material such that a flexible, solidified, endless, seamless backing loop having fibrous reinforcing material therein is formed. The flexible, solidified, endless, seamless backing loop formed has an outer and an inner surface. The step of preparing a loop of liquid organic binder material having fibrous reinforcing material therein preferably includes the steps of: applying a fibrous reinforcing mat structure around the periphery of a support structure, such as a drum; and winding one individual reinforcing strand around the periphery of the support structure, e.g., drum, in the form of a helix in longitudinal extension around the backing loop, i.e., along the length of the backing, in a layer that spans the width of the backing.
An alternative, and preferred method of preparing the endless, seamless loops of the present invention includes coating, i.e., impregnating, the fibrous, reinforcing mat structure with the liquid organic binder material prior to being applied around the periphery of the support structure. One method of impregnating the fibrous reinforcing material is to coat the fibers through an orifice with the binder material. If the organic binder material is a solid material, such as a thermoplastic material, the step of preparing a loop of liquid organic binder material having fibrous reinforcing material therein includes: applying a first layer of a solid organic binder material around the periphery of a support structure, preferably a drum; applying a layer of fibrous reinforcing material around the first layer of solid organic polymeric binder material on the support structure; applying a second layer of a solid organic polymeric binder material around the first layer of solid organic polymeric binder material and the layer of fibrous reinforcing material on the support structure to form a structure of a solid organic polymeric binder material having a layer of fibrous reinforcing material therein; and heating the solid organic polymeric binder material until it flows and generally forms a liquid organic polymeric binder material having fibrous reinforcing material therein. Herein, the term xe2x80x9cliquidxe2x80x9d refers to a material that is flowable or flowing, whereas the term xe2x80x9csolidxe2x80x9d or xe2x80x9csolidifiedxe2x80x9d refers to a material that does not. readily flow under ambient temperatures and pressures, and is meant to include a thixotropic gel.
The flexible backing compositions of the invention can be coated with adhesive and abrasive layers using any conventional manner. Typically, and preferably, this involves: applying a first adhesive layer to the outer surface of a solidified, endless, seamless, loop having fibrous reinforcing material therein; embedding an abrasive material into the first adhesive layer; and, at least partially solidifying the first adhesive layer. The abrasive material, preferably in the form of grains, can be applied electrostatically or by drop coating. In preferred applications, a second adhesive layer is applied over the abrasive material and first adhesive layer; and both the first and second adhesive layers are fully solidified.
Alternatively, the first adhesive layer and the abrasive layer can be applied in one step by applying an abrasive slurry to the outer surface of the backing. The abrasive slurry includes an adhesive resin and an abrasive material, preferably a plurality of abrasive grains. The adhesive resin is then preferably at least partially solidified. A second adhesive layer can then be applied. In certain preferred applications of the present invention, a third adhesive layer can be applied if desired.
Similar methods can also be used in preparing a coated abrasive backing using a support structure, such as a conveyor system. Such a system would typically use, for example, a stainless steel sleeve, in the form of a conveyor belt. In this embodiment, the step of preparing a loop of liquid organic binder material includes preparing the loop around the conveyor belt.